<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>01_页面版心</title>
    <style>
        .main {
            background-color: #00FF00;
        }
        .center {
            background-color: pink;
            width: 600px;
            margin: 0 auto;
        }
        .card {
            width:300px;
            height: 300px;
            background-color: deepskyblue;
            line-height: 300px;
            text-align: center;
            margin: 0 auto;
        }
    </style>
</head>
<body>
    <div class="main">
        <div class="center">
            <div class="card">我是内容</div>
        </div>
    </div>
</body>
</html>